In recent years, a need has arisen for high-performance polymeric materials in the development of electronic devices such as liquid-crystal displays, organic electroluminescent (EL) displays, touch panels, optical semiconductor (LED) devices, solid-state image sensors, organic thin-film solar cells, dye-sensitized solar cells and organic thin-film transistors (TFT).
The specific properties desired of such materials include: (1) heat resistance, (2) transparency, (3) high refractive index, (4) high solubility, (5) low volume shrinkage, (6) high moisture resistance at high temperatures, and (7) high film hardness.
The inventors earlier discovered that polymers containing recurring units which have a triazine ring and an aromatic ring possess a high refractive index and are able, with the polymer alone, to achieve a high heat resistance, high transparency, high refractive index, high solubility and low volume shrinkage, thus making such polymers suitable as film-forming compositions in the fabrication of electronic devices (Patent Document 1).
Of related interest, pattern formation using transparent materials is carried out in spacers, insulating films, protective films and the like in liquid-crystal display elements, and many negative-working photosensitive compositions have hitherto been described for such applications.
In particular, recently, with the increased demand for high-definition liquid-crystal displays and cell phone displays, there has arisen a desire for small patterns not more than 10 μm in diameter.
Also, in touch panels, to enhance the visibility of the transparent electrode, there is an increased need for a high refractive index layer. However, the presence of an insulating film in electrode wiring areas affects responsiveness, and so it is necessary to remove the insulating layer over a width of 100 to 1,000 μm from the wiring areas.
Existing materials used in this application are inadequate in terms of refractive index. Moreover, it is difficult to increase the refractive index above 1.7 while maintaining the transparency.
Although the polymer of Patent Document 1 is able to address such needs in terms of the refractive index, there remains room for improvement with regard to fine pattern formability.
Patent Document 2 discloses a pattern-forming composition that includes a triazine ring-containing polymer, but this polymer has a refractive index of less than 1.7 and is thus unsuitable for the above applications requiring a higher index of refraction.